Cell based therapy holds promise for treatment of neurodegenerative diseases such Parkinson's disease (PD), by providing replacement cells for dopaminergic neurons lost to disease or through neuroprotection of host tissue. There has been great progress in differentiation of dopaminergic progenitor cells (DAPCs) into replacement neurons as well as in transplantation of mesenchymal stem cells (MSCs) to rescue diseased host neurons. However, most animal model and human studies of PD rely on highly invasive intra-cerebral injections to deliver cell based therapy to the brain. Not only do such multiple needle injections pose risks of life threatening complications such as hemorrhage or infection, but their efficacy is usually limited by inadequate migration of cells from the needle track. New methods of cellular delivery that are both less invasive and have superior capacity to distribute stem cells in appropriate brain regions are needed. This study will explore and combine two novel strategies with potential for less harmful and better distributed delivery of stem cells to brain. Previous studies have used MRI guided focused ultrasound (MRgFUS) to produce minimally invasive, regionally targeted, safe, and transient opening of the blood-brain barrier (BBB) to enhance brain delivery of therapeutics. Ultrasonic treatment also enhances homing of human MSCs to target tissues, but has not yet been studied in brain. Potentially a dramatic improvement over current methods, FUS mediated BBB opening alone results in a relatively low efficiency transfer of therapeutics from bloodstream to brain. Another complementary technology could enhance efficacy of this transfer. Growing evidence (including our own work) shows that external magnets can influence the retention of stem cells loaded with superparamagnetic iron oxide nanoparticles (SPION) in brain. We will assess the capacity of external magnets to enhance brain delivery and retention of SPION loaded stem cells after FUS mediated opening of the BBB. We will also assess the role of homing in entry of cells into brain during this process. The goal of this first study of it kind is to develop a strategy to deliver stem cells to the striatum and improve brain structure and function in an animal model of PD using a safe, effective and clinically applicable method. Aim 1) To determine the capacity of an external magnet to enhance delivery and retention of SPION loaded stem cells from bloodstream to brain after MRgFUS mediated opening of the BBB. A) Although injection into the carotid artery is the most efficient route to deliver a blood borne therapy to brain, is this more invasive route required for stem cell delivery after FUS mediated BBB? B) What is the optimal design, strength and timing of application of the external magnet. C) Do cells enter brain after MRgFUS by diffusion through gaps between brain endothelial cells, or does FUS mediate changes to enhance cell adherence or chemo-attraction? We will compare the number and distribution of stem cells within striatum after FUS mediated BBB opening and magnetic attraction using two different types of human stem cells (neural progenitor cells or mesenchymal stem cells) with known differences in capacity for homing to injured tissue. These experiments will be performed with FUS alone and in combination with the application of powerful magnets applied to the head. Aim 2) We will then target the delivery of SPION loaded DAPCs or MSCs to the damaged striatum in a rat model of PD. The region of the affected striatum will be subjected to MRgFUS mediated BBB opening followed by injection of these two forms of beneficial stem cells along with application of an external magnet. Animals will be evaluated with histologic methods to assess DA differentiation and restoration of DA innervation, and for signs of functional improvement in motor behavior. These pilot experiments will determine the feasibility of this minimally invasive strategy to enhance stem cell transplantation for patients with PD.